1. Field of the Invention
The present invention relates to a hologram screen and a hologram display for displaying images by projecting image light thereon.
2. Description of the Related Art
As shown in FIG. 30, it is known in the art to provide a hologram screen 9 which is attached to a store display window or the like and displays moving or still images for advertising or other purposes.
The hologram screen 9 comprises, as shown in FIG. 30, a transparent member 91 and a hologram film 92 laminated to the transparent member 91.
The basic concept of the hologram screen 9 is as shown in FIG. 30; that is, image light 31 is projected onto the hologram film 92 from a projection apparatus 2 (for example, a projector) positioned below (or above) the rear side of the hologram screen 9, i.e., the side opposite from the side being viewed by an image observer E, and the image light 31 focused as images on the hologram film 92 is diffracted and scattered forwardly by the hologram film 92 thereby presenting the images for viewing by the image observer E.
The hologram film 92 used for the hologram screen 9 is produced by recording a scatterer on a photosensitive member in an optical exposure system.
However, the hologram screen 9 using the thus produced hologram film 92 has had the problem that the colors of the images projected by the projection apparatus 2 cannot be reproduced correctly, for example, the projected images appear somewhat greenish.
To investigate this problem, when the spectral characteristics of the hologram film 92 were measured and analyzed, as disclosed in Japanese Unexamined Patent Publication No. 11-202419, it was found that the image color reproducibility degraded presumably because the hologram film 92 has such a spectral distribution that its efficiency greatly varies depending on the wavelength of the diffracted light.
This led to the discovery that the color reproducibility of the images displayed on the hologram screen 9 improves when a certain degree of spreading is provided to the image light 31 incident on each portion of the hologram film 92.
In view of this, there has been proposed a hologram screen that uses the hologram film 92 in combination with a light scattering device constructed as a means for providing a certain degree of spreading to the image light 31 projected from the projection apparatus 2 and incident on the hologram film 92 (Japanese Unexamined Patent Publication No. 11-202417).
However, if the light scattering device is simply combined with the hologram film 92, satisfactory color reproducibility cannot be achieved.
On the other hand, it is also important that the hologram screen inherently be designed so that the image observer E can see the background behind the hologram screen 9 as well (see FIG. 3 and FIG. 6).
The prior art hologram screen 9 has the further problems that the color changes or the viewing area becomes narrower as the observer moves away from a direct ling of sight, and that, when the screen is constructed by joining multiple holograms, color differences occur at the joins.
Furthermore, the prior art hologram screen 9 has had the problem that, as the projection distance of the image projection apparatus increases with increasing screen size, the hologram device has to be remade to match the increased projection distance and the size cannot be increased by simply combining the same components together as with television sets. A production method for increasing the hologram screen size is disclosed in Japanese Unexamined Patent Publication No. 11-102153, but with this method also, the hologram device has had to be remade as the projection distance of the image projection apparatus increases.